For any conditional access transmission system, the switching time between channels is essentially dependent on the following:
the signal acquisition time, the service channel acquisition time, the service channel conveying all the information on the structure of the multiplex (position of the video component, number and position of the sound components, address of the ECM channel, etc.), the maximum waiting time of an ECM (entitlement message), the processing of the ECM (decryption and check of the rights), the return of the Control Word to the descrambler.
A known solution is described in the document U.S. Pat. No. 5,349,641 in which the ECM of the current channel is sent at a first rate, and the ECMs of the other channels are also embedded into the ECM stream of this channel but with a lower rate.
In the document WO 2009/092016, the solution proposed is to bundle the ECMs of different channels into one ECM and broadcast this bundled ECM into each channel.
This solution has the drawback of unduly loading the channel with additional data not directly useful for this channel.
In the document WO2005/020564, the system described scans the potential additional channels to extract the corresponding control words. Each control word is then stored into a memory and immediately available if the channel is selected by the user.
The drawback of this solution is that a specific tuner has to be designed to scan the other channels in order to collect the other channels' ECMs. This solution is limited to channels within the same band, the tuner being locked to this band to receive the current channel and unable to switch to another band without interrupting the viewing.
The document EP 0 740870 proposes sending a first message common to a plurality of channels from the same operator, this message having a root control word. Each channel has its own messages comprising the access conditions and a diversification value to calculate the channel's control word.